This invention relates to a high frequency arc welding method and apparatus and, more particularly, to a high frequency arc welding method and apparatus in which a D.C. electrical source used for welding purpose and either another D.C. electrical source or an equivalent capacitor, used for regenerative purpose of the electrical energy stored in the inductance of the arc welding apparatus and inevitable cable inductance are provided and the stored electical energy is regenerated in the D.C. electrical source used for welding by adjusting properly the voltage of the another D.C. electrical source or the equivalent capacitor, for regenerative purpose.
It is well known that when high frequency pulse component of 10 KHz to 100 KHz is involved in the welding current of a D.C. arc welding apparatus, the superiority in the stiffness and the stability of the arc to those without having high frequency pulse component is remarkable, irrespective of non-consumptive electrode type and consumptive electrode type, therefore the welding speed can be accelerated extremely, moreover the pulsing welding current makes beads neat and improve welding characteristics metallurgically. It is noted that the relationship between the high frequency arc current and the welding effectiveness is stated as (1) the higher the frequency of the high frequency pulse current the better the welding characteristics and also (2) the larger the ripple component involved in the high frequency pulse current the better the welding characteristics, with the mean value of the high frequency arc welding current kept the same.
Prior art of the high frequency arc welding apparatus is shown in FIGS. 1 to 4, in which FIGS. 1 and 3 are circuit diagrams of the prior art and FIGS. 2 and 4 show the waveforms of the welding current obtained in the circuit diagrams given in FIGS. 1 and 3.
In FIGS. 1 and 2, when a switch SW is closed, welding current i flows from a D.C. electrical source E through the switch SW, an inductance L of the welding machine and torch cable and a resistnace R which is equivalent to the arc load of the welding machine to the D.C. electrical source E in FIG. 1 and the welding current i leads up from a point 0 to reach a value at a time t1 through a time t0 in FIG. 2. After an on-duty duration of the switch SW elapses which is necessary to maintain the welding current at a mean value which is previously set, the switch SW is opened at the time t1. Then the welding current i flows in a circuit consisting of the inevitable inductance L, the arc resistance R and a diode D in FIG. 1 and the welding current i trails down from a value at the time t1 to a value at a time t2 to attenuate with a time-constant L/R. At the time t2 when a duration T0 elapses, which is determined by the frequency of the high frequency pulse current which is previously set, the switch SW is again closed and thereafter the open and close cyclic operation of the switch SW is repeated. Thus the welding is performed according to the waveforms of the welding current shown in FIG. 2.
Under these conditions, when the time-constant L/R of the attenuation is large, it requires a long time duration for the welding current to attenuate completely, so the ripple component of the welding current is made less, as shown in the waveforms of FIG. 2. Accordingly, a defect is noticed in this welding current in that said better welding effects with high frequency and large ripple component cannot be obtained, even if the loss is kept less.
In the circuit shown in FIG. 3, a resistance R0 is inserted in the circuit in which the welding current attenuates in order to improve the characteristics given in the circuit shown in FIG. 1. According to the circuit shown in FIG. 3, the time-constant of the attenuation will be denoted as L/R+R0 which is less than that given in the circuit shown in FIG. 1 and also the ripple component of the welding current is made larger, as shown in FIG. 4, than that shown in the waveforms of FIG. 2. Thus, an advantage is obtained in which a better welding effect is expected due to the larger ripple component. However, another defect is noticed to be fatal to the welding operation in this circuit in that the operational efficiency is deteriorated through a huge energy consumption due to the inserted resistance R0. When the pulsing frequency of welding current is 25 KHz and the peak value of welding current is 1,000 A and the inevitable inductance L is 5 .mu.H, the energy consumption of R0 exceeds 60 KW in the case of FIG. 4.